How do you clean old ceramic floor tiles to reuse?

Soak them in a sinkful of hot water and white vinegar overnight. Next day clean off as much as you can by hand and with a wire brush attached to a drill. Keep soaking and cleaning until they are ready to use. They don't have to be perfect but close.

When using wire wheel on drill, be sure to wear mask and safety glasses. Try to do grinding outside.

Chuck